Endocrine Hypertension: Differential diagnoses in

hypokalaemic hypertension

Calvin Chong

Chemical Pathology, PMH

Significance

• Relationship of hypokalaemia and endocrine hypertension

• Medicolegal concerns

oGuidelines available (but are they read?)

Investigations

• Aldosterone-renin ratio

• Overnight dexamethasone suppression test

• Balance study

• Adrenal venous sampling

Investigations

• Renal function test

• Venous blood gas

• Transtubular potassium gradient

How to investigate hypokalaemic hypertension?

• Never a problem even in medical student examination

• Always a problem in clinical practice

• Problem: Not doing the tests

Investigations in hypokalaemia

• Repeat renal function test

• Venous blood gas

• Urine potassium

• Transtubular potassium gradient

Hypokalaemia

Hypokalaemia

Hypokalaemia

Venous blood gas will do –no need for arterial puncture

Instead of doing it in two steps, do the thing in one go.

Hypokalaemia

Investigation of renal tubular acidosis is complex and may

need dynamic function tests –consider referring to renal units.

Hypokalaemia

Extra-renal loss –Could it be due to drugs?

Hypokalaemia

Renal loss – mineralocorticoid excess syndrome must be

considered.

Hypokalaemia

If it is transient, does it mean that it’s not sinister?

Phaeochromocytoma may present like this!

TTKG

• Transtubular potassium gradient

o (Urine K/Plasma K) ÷(Urine osmolality/Plasma osmolality)

oNormally 3-7, a dimensionless value

• In hypokalaemia, expect < 3

• Reflects mineralocorticoid action

TTKG

• To be interpretable:

Urine sodium >= 40 mmol/LUrine osmolality > Serum osmolalityNot on potassium supplement

Mineralocorticoid excess syndromes

Investigations

• Aldosterone-renin ratio

• Overnight dexamethasone suppression test

Aldosterone-renin ratio

• Out of bed for >=2 hours

• Seated for 5-15 minutes

• Unrestricted salt intake

Discussions

Thanks!